The root cause is branding. “Linux” (the brand) is muddy, confusing, and unfriendly to the mainstream computer user: those on the other side of the chasm. They are the exact people that we need to embrace Ubuntu and they don’t *get* “Linux”. They don’t know what it is. They get a negative connotation when they hear the word. Don’t believe me? Ask your non-techie friend or loved one. (I just asked the person beside me and the response I got was less than flattering.)
Sadly the same can be said more and more for Ubuntu these days. Go ahead and define it. It gets muddy *very* quickly as well.